a) Field
The subject matter generally relates to geothermal vertical heat exchanger systems. More particularly, it relates to a pipe spacer for separating a U-bend pipe in a bore during installation of a pipe.
b) Related Prior Art
At this point, in the field of geothermal heat exchanger systems, a closed loop geothermal heat exchanger (GHX) is used to extract ground thermal energy. It is well known in the prior art that heat exchange occurs by the circulation of a fluid in a pipe or tube composing the closed loop. Usually, the pipe has both a supply and a return, which are normally located in the same bore hole. The supply and return pipes are connected via a “U” shape joint (U-Bend) at the bottom of a bore hole. In fact, because a vertical GHX is normally made up of High Density Polyethylene 3408 (HDPE 3408) piping, the pipe has a certain elastic flexibility thus, during the installation of a vertical geothermic exchanger, gravity tends to force the pipes to curve or bend, interlace and to lean against themselves or against the bore hole wall at their curvature or bending points. There is therefore a need in the art to provide a pipe spacer for easily separating a U-bend pipe in a bore during installation of pipe.
The scale of a geothermic field is dictated by the following elements:                1. Thermal loads to be dealt with (Building, process, etc.);        2. Underground geological conditions (soil and rock type, density, water content and average temperature);        3. Design temperature of the GHX liquid used;        4. Bore hole geometrical configuration; and        5. Pipe and grout thermal properties.        
For environmental and technical reasons, it is normally necessary to fill the space around the U-Loop with a grout mixture. This grout represents an additional thermal resistance. Any grout located between the pipe and the bore hole wall causes a decrease in heat exchange which results in a decrease in the bore hole's energy efficiency and thus requiring an increase of the bore hole's length.
Interlacing, as well as the U-Loop supply and return piping proximity, contribute in reducing the geothermic exchange effectiveness (heat exchange with the ground) by increasing the thermal interference between the two pipes (supply and return) of a bore hole and by creating contact points between them, i.e. thermal energy is partially exchanged between the pipes and not entirely with the ground. Consequently, this decreases the bore hole's energy efficiency and requires an increase of its length or an increase of the number of necessary bore holes.
For a given project with specific thermal loads, at a determined site with specific geological conditions, there are few elements one can influence in order to optimize the design and the thermal effectiveness of a geothermic field. One of these elements is the pipe spacing within a bore hole.
In order to maximize heat transfer effectiveness, it is necessary to space apart as much as possible the supply pipe from the return pipe. This reduces their reciprocal thermal interference while reducing the induced grout thermal resistance.
Known in the prior art to create spacing in between pipes is U.S. Pat. No. 6,000,459, which is entitled U-BEND PIPE SPACER. This model used in North America is known under the name GeoClip™. A GeoClip™ is a spring loaded spacer. It accomplishes its task as a spacer, to maintain pipes diametrically opposed, via a spring exerting a dynamic pressure on the pipes in question, so that the GeoClip™ can push on the pipes. Because a Geoclip™ is composed of four (4) main mobile parts, two (2) retention cavities or clips to receive the pipes, one (1) spring to exert a force of repulsion and one (1) retention ring to hold the spring closed before its use, prior art spacers such as the GeoClip™ are complex to manufacture. This complexity of the prior art GeoClip™ spacer renders its utilization difficult and unpleasant. Moreover, it is characterized by its fragile nature which is inherent to its design.
It is also common to find “broken” GeoClips™ on geothermic system construction sites. Once the spring is released from one of its anchoring points, the GeoClip™ becomes useless. Although the GeoClip™ is intended to space apart u-bend pipes during installation in a geothermal system, it is very difficult to install and slows down tremendously the speed of installation of pipes which make it less interesting to handle.
Moreover, there is shown that prior art spacers often result in a significant amount of rejected, yet functional and in good condition, spacers on geothermic system construction sites. For example, from the way the pipes are connected to a GeoClip™, it happens often that one of the two pipes detaches before insertion of the GeoClip™ into the bore hole. The spring of the GeoClip™ then expands completely, thus opening the spacer. The necessary time and work to reset the spring and to reattach the GeoClip™ to the pipes is greater than the value of the GeoClip™ itself. Consequently, the worker simply tosses the GeoClip™ aside and replaces it with a new one.
On the other hand, it is also common to find prior art spacers or GeoClip™ retention rings scattered on geothermic system construction sites. These retention rings are useless and non reusable once removed from a GeoClip™. These rings, which are non biodegradable, are often found buried on the construction site, creating unwanted pollution. Existing, other spring-loaded spacer prior art comprises a metallic spring that rusts over time. This rust can lead to microbial growth. Once inside a borehole, such rust is a vector for aquifer contamination. There is therefore a need in the art to provide a simple pipe spacer device for easily separating a U-bend pipe in a bore during installation of pipe.
Additionally, due to the shape of prior art spacers such as GeoClip™, and its method of use, the bore hole must be filled with a geothermic grout at the time of the GHX insertion. The GeoClip™ retention ring is foreseen to remain in place not only until the supply and return pipes of the geothermic exchanger are connected to the GeoClip™, but also until the tremie pipe is positioned in its predefined place on the GeoClip™. The tremie pipe is used when filling the annular space between the exchanger and the bore hole wall with a geothermic grout. This pipe is connected to the GeoClip™ in a way so as to prevent the GeoClip™ spring from extending once the retention ring is removed and as long as the tremie pipe itself has not been withdrawn.
In such configurations, it is impossible to descend the tremie pipe if it is not descended at the same time as the GeoClips™. This creates a drop in bore hole drilling productivity as well as a need for expensive coordination, since the drilling and the grouting teams, which do not work at a similar pace, must however wait after each other for each bore hole. For example, drilling one bore hole typically requires 12 hours of work, while the loop insertion and bore hole grouting typically requires 4 hours of work. This adds additional costs for any installation project. Other prior art spacers such as the GeoClip™ require the use of both hands and several handling steps in order to position and connect the spacers to exchanger pipes. There is therefore a need in the art to provide a pipe spacer device for easily, and in a short period of time, separating a U-bend pipe in a bore during installation of pipe.
Finally, the complex handling requirements of prior art spacers such as the GeoClip™, in addition to the risks of their detaching from a pipe before and after their insertion in the bore hole, make prior art spacers unattractive with respect to their use with several heat exchanger installers.
Consequently, there is a need for a pipe spacer to address this requirement for reducing thermal interference while reducing induced grout thermal resistance. Moreover, there is also a need for a spacer which can improve a driller's productivity by reducing risks and facilitating installation work in general.
For all these disadvantages, there is therefore a need in the art to provide a pipe spacer for easily separating a U-bend pipe in a bore during installation of pipe, developed for use in geothermic systems using closed loop heat exchangers. More particularly, the pipe spacer will need to maintain the GHX pipes as close as possible to the bore hole wall in which the exchanger is placed. This increases the energy performance of the GHX, reduces length of pipes required and substantially reduces installation time and costs.